A previous reseller of the Ionovac in Germany, Otto Braun (1928-2020), created an updated plasma tweeter in 1978. His company Corona Acoustic developed the Corona types 314-514 based on Klein's work. A slight misnomer as this was a glow discharge plasma tweeter and not a corona discharge based speaker. It is similar to the Ionovac in that a plasma is created in a quartz tube which is horn loaded and driven by local circuitry at the rear. The description of its operation differs from what may be found here for plasma tweeters as it doesn't include any thermal characteristics in the explanation, it is described more closely to an ion wind speaker. That doesn't quite fit the physics and is an example of how the mechanisms can be misunderstood.

This plasma tweeter has had one of the longer lifespans of a massless speaker as the production of it was taken over in 1998 by Lansche Audio who still sells it. Acapella (formerly ATR) also have a current model, the Ion-TW-1, which was also originally designed by Otto Braun. That is now sold as part of their high end loudspeaker systems. None of these appear to have obtained patents or licensed their designs, which would make sense from the amount of prior art as they are an extension of Klein's work.

Around the same time, in 1978, the Hill Type-1 Plasma Speaker System from Plasmatronics Inc. was demonstrated in the US, patented in 1979. This well known commercial product developed by Dr. Alan Hill, often known just as the Plasmatronic, was a full range speaker system using a unique plasma tweeter based on a DC bias system instead of RF and with several plasmas rather than being horn loaded. Notorious for its use of helium tanks in the speaker cabinet, the helium was gently flowed into the plasma tweeter chamber reducing some noxious gas production but not eliminating it as the plasma is in an open cell. Hill has claimed (relayed later by his assistant Tony Silsich) that the helium was primarily for improved sound reproduction and not the reduction of ozone or NOx.

The Hill Type-1 was reviewed well in articles from Popular Science (1979), International Audio Review (1980) and Stereophile (1980) but with most mentioning how the large helium tanks may be a major downside. Only a few sold but it definitely goes down as one of the best looking tweeters, although the rest of the speaker cabinet and dynamic bass drivers were rather more conventional. A reconditioned tweeter unit has been demonstrated at AXPONA 2023.

Another notable but rare commercial design that was not based on a Klein RF circuit is the IML DVL Digiplasma, released around 1981. This was a unique PWM (pulse width modulated) design with a nice large open dual glow discharge plasma. It would seem to have had no mitigation for the toxic gas production.

Along with the Magnat mentioned previously, the late 70s and early 80s could be seen as the hay-day of plasma tweeter commercial competition.

Part 5 - Don't Breathe

Plasma Speaker and Tweeter Ionophone Information

Plasma Loudspeakers

Ionovac and Plasmatronic

Plasma Tweeters

Plasma Speaker

Corona Wind or Ionic and Ion Speakers